i did exactly the same thing that you did. i exchanged my canadian driving license for an automatic-only
uk license. and i too drove a manual transmission car in canada (for 16 years!).
i ended up taking the
uk driving test. actually, i just did it this morning. and thank god i passed on the first go (*sleepy punches the air*).
i spoke to the examiner about alternatives to being re-tested in the
uk and i mentioned the possibility of re-taking the test in canada on a manual transmission car. he was very skeptical that it would work. also, i've never heard of anybody being able to do it successfully. so, i think you're just gonna have to take the
uk test, or just stick to automatic transmission cars.
the test isn't too bad. it's virtually the same as it is in canada. i did about 10 hours of practice with an instructor. that helped a lot. i probably would have failed if i hadn't gotten myself accustomed to sitting on the right side of the car, and driving on the left side of the road, and dealing with those big multi-lane round abouts in heavy traffic.
i think i got a bit lucky with the examiner. he was super friendly and we chit-chatted throughout the test about canada and stuff. it was weird... it was as if my passing the test was a forgone conclusion and we were just going through the motions. perhaps they're a little more lenient when it's obvious you know how to drive (smooth driving, clutch control, gear changes, etc.), but i wouldn't assume that.