Thursday night's junior middleweight world title fight between Mary Spencer and Mikaela Mayer has this week been upgraded to a unified championship bout.

WBA beltholder Mary Spencer (10-2, 6 KOs) will defend her strap, while the WBC and WBO titles recently vacated by the retiring Cecilia Braekhus will also be on the line in their Montreal Casino main event.

Spencer-Mayer headlines a card featuring an all-Quebec super middleweight matchup between Ring ambassador Wilkens Mathieu (14-0, 10 KOs) and Shakeel Phinn (27-3-2, 17 KOs), with select undercard bouts streamed on Top Rank Classics at 8 p.m. ET/5 p.m. PT.

BoxingScene were first with the news after receiving confirmation from Eye of the Tiger Management, the event's promoter.

Former long-reigning welterweight champion Braekhus (39-2-1, 9 KOs), who finished her career as a two-division titleholder having outpointed Ema Kozin on October 4, said farewell on a historic stint in the paid ranks after turning pro in 2007.

Spencer, a 2012 Olympian, will make the second defence of her WBA strap after being upgraded to full champion following a 10-round points win over Naomi Mannes 13 months ago.

IBF beltholder Oshae Jones (9-0, 3 KOs) has won and since defended her 154-pound title with split decision victories over Femke Hermans and Elia Carranza over the past year, though there's no update on a return timeline for the 27-year-old.

Mayer represented the U.S. during the subsequent Olympic cycle and enters their contest as the current WBO welterweight champion, having failed to secure a full agreement for an undisputed matchup with Wales' Lauren Price this summer.

Mayer posted on her social media channels she was travelling to Canada on Monday, with this news breaking overnight.