The start of Canada's Gold Cup camp was overshadowed by three of Vancouver Whitecaps' internationals falling ill in the aftermath of its CONCACAF Champions Cup final defeat to Club America.

That prompted Jesse Marsch to claim the Whitecaps camp had been targeted by a "poisoning", but his players showed no ill effects against Ukraine.

Canada's record goalscorer, Jonathan David, struck twice inside the first 24 minutes, tapping home after a goalmouth scramble then sending a glancing header into the top-left corner from Tajon Buchanan's corner.

Promise David added a third 31 minutes into his Canada debut, dispossessing Ukraine's Valerii Bondar then finishing coolly under Anatolii Trubin.

Buchanan flicked home nine minutes from time as Canada continued to put its opponent to the sword, although Illia Zabarnyi and Oleksandr Zinchenko made the scoreline more respectable with late goals for Ukraine.

One of Canada's foremost rivals at the Gold Cup, Mexico, was on the wrong end of another six-goal thriller, against Switzerland in Salt Lake City.

Switzerland fielded a strong team and went ahead when Breel Embolo rounded Raul Rangel to tap into an empty net after 20 minutes, the only goal of the first half.

Early in the second period, AC Milan's Santiago Gimenez equalised with a scrappy header, but substitute Zeki Amdouni soon swept home to restore Switzerland's lead.

Bologna's Coppa Italia hero Dan Ndoye extended the visitors' lead, and although Angel Sepulveda fired inside the near post to make it 3-2, Fabian Rieder completed the scoring in the 90th minute.

Canada opens its Gold Cup campaign against Honduras in Vancouver on 18 June (AEST), three days after Mexico faces Dominican Republic in the opening match of the tournament.