I am British and had my British driving licence.
Here is my experience:
1) if you are a qualified driver, your brain will adjust (adapt) quickly to the shift from left to right road driving skills. This is not an issue at all but common sense.
2) if you are a driver, you don't necessarily need driving lessons. You only need to set in the passenger seat and observe how your friend or relative can drive in Canada.
3) the road signs, roads and trafic signals are slightly different in Canada compared to Britain. So you have to observe and ask. For example, the round abouts are the main landmark in British traffic. the round abouts are rare or even do not exist in Canada. in some junctions, where there are no traffic lights, it can be confusing and difficult to go through. Also I found it confusing to get used to 4 or 3 stop signs in some street junctions. Another example, in Canada when the light is still RED, ahead , you can turn right if it is safe and clear to do so. It makes sense. in England, you can not turn left (equal to turn right in Canada) unless the light ahead is turning green......this does not make sense. In some junctions, you can turn left when it is green and safe, but in other junctions you have to watch for the green arrow. This is confusing sometimes.
4) traffic lights are higher, so you have to get used to adjust your head to look up. traffic lights in England are ahead of you, lower and easy to catch. The traffic signs are smaller in Canada and most streets and hospitals are not well sign posted compared to England.
5) almost all cars in N America are automatic..rarely you come across a manual car. The opposite (manual) is the case in Britain. if you can drive a manual you can easily shift to automatic but you may gradually forget your manual skills when you go back home. I doubt very much if an average Canadian would be able to drive a manual car in Britain. It makes sense that if you pass the driving test in manual then you are automatically licensed for the automatic, which is the case in Britain. In Canada you pass the test in automatic and you are licensed for both, which, in my experience is so dangerous.
6) driving and drivers in N America are more agressive compared to England. the roads in England are designed to make it easy and safe to join the main stream traffic. it is not the case in Canada. For example, the slippery roads to the main roads or highways in England are long, safe and make it easier to gradually slip into the stream. There are waring signs for you as a driver through the slippery roads and to those in the high way or main stream to give way. It is not the case in canada. so be careful.
Finally, I will try to remember other experiences and post it here, if I missed it