You might not need much fertilizer over the winter in canada as you likely won't see much growth. You should be fine using your liquid fert as foliar if you reduce the concentration. I believe I've read foliar fert is absorbed at 10x the rate compared to through roots, so you'd use 10% of the concentration. Also I've heard foliar feeding of iron-containing fert isn't recommended. I've done foliar feeding with a liquid fert that contains a small amount of iron though with no issues. I don't know what a safe amount is, could never get a clear answer.