what are the differences between NFL and CFL football (thick british viewer)?

There are quite a few differences. NFL: the field is 100 yards long by 53 1/3 yards wide, and the end zones are 10 yards long. CFL the field is 110 yards long by 65 yards wide, and the end zones are 20 yards long. There are different rules, one of which in the NFL you have 4 downs to advance the ball 10 yards before turning it over to the other team. In the CFL you have only 3 downs. There are other rule differences, too many to go into in this format.

Much, much more difference than the differences between Rugby League and Rugby Union.

One difference is that the field is wider in the CFL, which results in more plays for the Offense. Another one is that a player on the Offense, with the ball in their possession, may have a running start toward the scrimmage line.