London - The Canadian Grand Prix could determine whether Red Bull decides to stick with Renault, which powered the team to all of its Formula One championships, or switch to Honda engines from next season.
Team boss Christian Horner said after Sunday's Monaco Grand Prix, won by his Australian driver Daniel Ricciardo, that a decision would have to be made by "end of June, beginning of July".
"We're waiting with great interest to see the relative performance of engines in Montreal in two weeks' time," he added.
Canada, on June 10, is the seventh round of the 21-race season and both manufacturers are planning to bring major upgrades to the Circuit Gilles Villeneuve.
Red Bull, whose Renault engines are branded Tag Heuer, has won twice this season but the team has had a rocky relationship with the French company since the start of the V6 turbo hybrid era in 2014.