I think if you choose variable rate, it will help your DCR for the next purchase? Because with the same amount of mortgage, you will pay less payment every month, so your debt is lower, and you can approve for more the next purchase. Let me know if I am wrong.
Also, one thing we need to keep in mind is that the bank prime rate is 2.25%, and bank of Canada overnight rate is only 0.25%. When the overnight rate goes up 2% to 2.25%, would prime rate goes up 2% to 4.25%? How about 3%, 4% more...I remember the bank prime rate usually only 0.5% higher than the overnight rate. Just a thought.