Be aware that an IDP (International Driving Permit) is nothing more than a TRANSLATION of your home driver licence into various other languages. It does not confer any rights to drive a vehicle. You must always present your original (home) driver licence along with the IDP if you are asked to show a driver licence.

Given that the UK uses the same language as most of Canada, you really don't need an IDP there. It doesn't hurt to have one, but don't think for a minute that the IDP is a licence. It's not - it's just a translation document.

Apropos of learning to drive on the left side of the road, you will find that as long as there are other cars around you that remind you of which side of the road you should be on, it's not very difficult to make the transition. Where you have to be extremely careful is when there are no other cars on the road. That is when you will be at the greatest risk of slipping back into "automatic pilot" mode and reverting to driving on the wrong side of the road (meaning, the wrong side in UK terms). An especially dangerous time is when you are leaving a parking lot or gas station and entering a roadway and there are no other cars around... you have to really concentrate on making sure you look in both directions before you enter the roadway, and that you establish yourself on the correct side (the left side) of the roadway once you leave the parking lot or gas station.