PM Carney ran (and won) on a platform of not giving in to Trump's manipulative tactics, of keeping Canada strong and independent, of protecting Canada's best interests. Now the author (Charlie Angus, btw) is asking him to keep those promises, to be the strong prime minister he said he would be, and not back down from what he said he would do.
Hope that helps.
There's a lot more than just the 51st rhetoric, and not all Canadian politicians have been proving they have a backbone.
See: Danielle Smith, Scott Moe, Pierre Pollievre, and Andrew Scheer, among others.