Bouchard will be relying on him for guidance at the BNP Paribas Fortis Diamond Games in Antwerp, Belgium, on Monday.
A spokesperson for Bouchard's agent confirmed Sumyk's hiring to The Canadian Press on Friday.
The seventh-ranked women's singles player in the world parted ways with long-time coach Nick Saviano in November.
Sumyk has a wealth of experience, most recently coaching former world No. 1 Victoria Azarenka at the Australian Open in late January.