I agree with your GDP analysis but that's thinking like an economist which Trump is not (remember Trump's "Drill baby, drill?). Trump thinks in terms of personal wealth and how he can become wealthier.
Why did Trump want to buy Iceland? It had nothing to do with GDP.
It's about gaining personal control of Canadian resources in the same manner as one sees with Russian oligarchs. Putin wasn't thinking of increasing Russia's GDP when he captured Ukraine's offshore oil&gas platforms during his invasion of Ukraine.
Canada ranks fourth of countries by value of its natural resources (including coal, timber, natural gas, uranium, precious metals such as gold). It has the world's third largest oil deposits and ranks fourth in terms of natural resource value following Russia, US and Saudi Arabia.