Armed with a sunny Las Vegas backdrop and another gruelling training session less than an hour away, Mikaela Mayer is just days away from her latest test.

After winning an entertaining two-fight series with Sandy Ryan to wrestle away and retain the WBO welterweight world title, the two-division world champion has her passport ready as she moves up in weight once more.

She travels to Montreal, Canada this week to face WBA junior middleweight champion Mary Spencer (10-2, 6 KOs) in an October 30 headliner, exclusively broadcast on Top Rank Classics in the U.S. from 8pm ET/5pm PT. This week, their matchup has officially been upgraded to a three-belt unification with recently-retired unified champion Cecilia Braekhus' WBA/WBO titles up for grabs, adding further gloss on an compelling contest.

It's not quite the undisputed matchup she was hoping to secure with Lauren Price (9-0, 2 KOs), but serves as a solid consolation prize in the meantime and one the 35-year-old believes will bode well entering this late stage of her career.

Following the well-documented fallout from Ryan (8-3-1, 3 KOs) joining her gym without prior notice and training under her existing coach in Kay Koroma, while she steadily worked her way up openly looking for world title bouts at 147-pounds, a marketable feud unfolded.

It got ugly in parts, much like Alycia Baumgardner before her, but this time Mayer came out on top and there could be no complaints after a more comprehensive victory in their March 29 rematch.

"I didn't get the rematches I wanted in my career but fans wanted to see it again and that's the fighter I am," she told The Ring.

"We wanted Lauren for undisputed afterwards but the promoter logistics and networks we're dealing with meant it wasn't possible, so Top Rank had three options: I could fight at a lower weight [140-pounds], defend against someone no-one knows, or go up to 154 and challenge a champion. That was the best option for me, Mary was available and this will make me a stronger competitor."

After her commanding points win over Natasha Jonas on March 7, Price picked Mayer to beat Ryan in their rematch and spoke of a willingness to travel to Las Vegas to watch ringside, setting the wheels in motion for a finalised deal.

Her promoter Ben Shalom told The Ring last month the Olympic champion sustained a 'minor injury' and they plan to welcome her back late this year, though Mayer disagreed with the suggestion she was unwilling to box in Cardiff to get a deal done.

"We had the fight date, money and location set for July 26, it was supposed to be Top Rank's final fight on ESPN and would've been great. I won't bash Price because she wasn't fully informed with the negotiation process - I am - my manager George Ruiz includes me from start-to-finish and not every boxer is as lucky as me.

"Lauren didn't want to go to America and I don't blame her, I think they lowballed her but it backfired ... I had to move on. I wanted three fights this year, now it'll only be two, stay-busy fights don't interest me but even though I'm moving up again, I have the experience, skill and taken the time to put on weight and muscle, making me better when I do fight Price."

Mayer (21-2, 5 KOs) could conceivably still be an undefeated champion seeking a title in her third weight class, but suffered a pair of 10-round split decision defeats to Baumgardner and Jonas during her four-fight spell on British shores.

She accepts while physically capable of moving down to junior welterweight, MVP's recent signing spree means the promotion would've wanted her to join them before signing off on a potential big fight - a non-starter in negotiations.

"They just weren't willing to work with me otherwise and that was obviously not possible, so I looked in other directions. As a smaller welterweight, going up helps me to build strength and get that experience against physically stronger girls, props to Mary for taking it and I'm staying busy, which is what counts."

As such, it means a potential future fight with Olympic teammate and reigning heavyweight champion Claressa Shields remains a distinct possibility.

"We always agreed to 154 and I said I'd meet her there, it's on Claressa's terms and whether - or when - she wants to take her time to work down to that weight. We're both game and we'll see but I'm focused on Spencer, then Price for undisputed at 147. That will give her time to decide what she wants."

Mayer is a -600 (1/6) favourite to prevail among most oddsmakers, while Spencer is a +450 (9/2) underdog. Just based on their professional pedigree alone, it's easy to see why.

She told several outlets of a desire to depart the sport in two years' time, the end of 2027, though backtracked in saying it was a fluid decision and one impacted by feeling her best under head coach Kofi Jantuah.

Jantuah, 51, twice challenged for IBF world titles at junior middleweight and middleweight in the mid-2000s against Kassim Ouma and Arthur Abraham but fell short in wide points defeats against both.

The Ghanaian, who now calls Las Vegas home, is a hard-to-please disciplinarian who also trains highly-rated lightweight prospect Curmel Moton (8-0, 6 KOs) and has method behind his challenging training methods - many potential pupils are unable to withstand them.

But it's more complex than just showing tough love.

"I can't stress enough, how much it's a blessing to have Kofi. I wish I met him five years ago, I'm learning so much," Mayer said.

"He really broke down my mechanics. I wasn't throwing punches properly, which was breaking me down and hurting, little things, rotating more into shots, taking so much strain off and using my hips more. I'd been with coach Al Mitchell for 17 years, his way of wanting me to box got me very far but sometimes you need fresh eyes to shake up your brain and add new things."

Mayer has undergone several cortisone shots over the last few years, elbow tears and the like, as she had a 'ton of problems' with her right arm but shouldered through the pain without knowing it could be remedied.

"When it comes to combinations, mechanics, the way we train, I've never trained this hard in my life. It's not always hard work or overtraining, but we're constantly working in the gym, not taking time off between fights. People might get comfortable with their team but having someone completely change everything up, there's absolutely no cutting corners."

Jantuah finished his career with a modest 65% knockout ratio but scored knockouts in 12 of his last 14 fights stateside, going from defending Commonwealth welterweight champion in Ghana and the UK to bonafide world-level contender under promoter Lou DiBella.

"He was a big puncher and knockout artist, so he teaches you how to get power out of your shots without loading up and straining yourself. We do a lot of shadow boxing - almost an hour a day - he tells me it's not a warm-up, it's part of the workout but that's how you find your style, loads of repetitions, it's not about doing rounds. We're working on the bag for one or two hours at a time, it's not about conditioning, we're learning and developing skills.

"I've been in camp the whole way through from May, working Monday-through-Friday but not breaking down my body, just perfecting things. I wasn't sparring but we started picking things up in August, doing two-a-days [two workouts a day], I know how to get in shape, just want to continue getting better."

It's not London, Liverpool or Manchester this time around as she stresses there's no need to acclimatise, Montreal a mere four-hour trip away. Ontario-born Spencer is back among home comforts at Montreal Casino, knowing she needs to produce a better display than consecutive decision defeats by former IBF beltholder Femke Hermans.