Canada is also a very good place for hourbuilding. In the UK, even though you have a lot of uncontrolled airfields, you don't have many unmanned airfields. Flying into unmanned airfields for the first time is really a learning experience. You finally realise what overhead joins are for. You have the sole responsibility of determining wind direction, what altimeter setting to use, checking the runway condition. And this applies to both IFR and VFR.
You also become more weather savvy. In the UK many pilot's wx briefs consist of a quick glance at Met 214/5 and a couple of TAfs. In canada, there are many areas where forecast coverage is not great and go/no-go decisions require a bit of effort on the part of the pilot. You need more than a basic understanding of wx if you're going to fly in mountainous areas.
As has been mentioned above, flyng in INTL airports can be a bit unnerving at first. Its hard to explain the adrenalin rush when you're on a practice ILS approach with an A320 on you 6 O Clock and ATC is creaming at you to keep the speed up.
There is a lot you can learn in the US/Canada that you'll never learn in the UK, e.g flight plans/how to use the red knob.