I think that most, reasonable people appreciate that not every American (or person living in America) is a Trump supporter or otherwise lamentable.
I also agree and acknowledge that people in the UK, Canada, and elsewhere can have unfairly anti-American attitudes. That's likely a result of the power and influence of the US, and our cultural exposure to it. That doesn't make it right but, were UK politics more often a headline news item in the US and if UK cultural exports were as prevalent in the US, as US ones are in the UK, the reverse would likely happen.
I'm sure that many of us are grateful for the efforts of those Americans pushing back on Trump but, again, (1) many people will stand up for their own country against an aggressor, and (2) it's unreasonable to expect others to bear the harm, without complaint, that will arise in the interim.
I do also think that when Trump is centring US financial interests, in lieu of international cooperation, then the most sensible retaliation is an economic one. If the boycotts were to put a noticeable dent in the US economy, that has a far more likely chance of seeing Trump pressured to reverse-course than empty moralizing and complaints.
FWIW, I've seem quite a lot of Americans saying that they too will make a greater effort to buy Canadian, in solidarity. Those efforts are, of course, greatly appreciated.