They will ask that, but there’s often space to explain because of things like this and political prisoners. I’m not sure how Canada’s forms work and if he was convicted of something closer to selling multiple pounds to minors than simple possession*, that probably wouldn’t fly no matter what, but it’s definitely worth a shot.

*intent to sell is also determined very differently in different countries- in Germany, for example, having a scale stored with your supply or having multiple strains of weed in separate bags would not bump you up to intent to sell, but it does in the US