That is an interesting question. If you have your driver's license exchanged in Great Britain and that license is the exact same license that residents of Britain would receive, I don't think you would have a problem at all. However, if you have less than 2 years of driving experience, regardless if they accept your exchanged license or not, you'll need to wait until you have 2 years of driving experience total to complete the first road test. So this means, if you're coming from Italy or Great Britain and you only have 20 months of driving experience under your belt, regardless of the license you provide (Britain or Italy), you'll have to wait 4 months until you have a total of 24 months to take the road test. You'll be able to drive with a G1 in this time (a "learner's permit" type license).
If you DO have 2+ years of driving experience, they'll exchange your license from Great Britain and you'll be good to go, fully licensed. They can also accept your license from Italy with some additional processing on your part. If you bring your license from Italy and you have 2+ years of driving experience, you'll be required to take an eye exam & a written exam regarding the laws of the road. You'll then be able to immediately take your road test to receive your full license. So, if you are going to need to write an exam or take a road test in Britain to exchange your license, you might as well wait and just do that here in Ontario.
I hope that wasn't too confusing. Here's a link for more information https://www.ontario.ca/page/exchange-out-province-drivers-licence