It's really about what Nissan Canada, and Nissan corporate in Japan, want to do. VW for example shipped eGolfs to North America from the Wolfsburg plant, even though all other Golfs for this market (except for the R) normally are made in Mexico to keep the costs down.
Now whether it's cheaper to do so, vs. any possible tariff, is a different story. The Leaf's article in Wikipedia is saying that an 18% drop in price was possible for the US due to it being produced here, even when you factor in the costs of starting a whole new production line. I also don't know how constrained production is at the Oppama plant (where the Leaf for Japan is still being built) and if they have room once again to produce vehicles for other markets.
It's also possible that Nissan Canada might shift some burden of any additional tariffs from lower-profit cars to higher-profit trucks and SUVs.