Canada Post has a slight variance on envelope sealing, so be extra careful not to incur a surcharge here.  A variance of 25mm (1 inch) can be handled on machineable mail through the machines.  If it goes any further along than that and the flap is not sealed, you could be looking at a per piece additional charger for your entire mailing.  Make sure to try and seal the entire length of the flap to avoid this probability.

Let us know if you have any specific questions on this!