They absolutely would benefit.

Mr. Hypothetical lord high executive oligarch can take his private jet to Canada and lounge around on the company card with the money from his US company’s car sales, or find an excuse to convert some of it to USD for some reason, or use it to buy up more Canadian companies to expand their power, or a million other things.

However, I think the point of the boycott is more about making the tariffs hurt the US economy by messing with their ability to export as well as import. Making the trade numbers look bad is likely to put more pressure on the US to end the trade war. It’s not so much about hurting the capitalists that operate in Canada (a worthy goal in itself but not what people are specifically trying to do in this instance since it won’t really affect those trade numbers).