Having almost completed a repower on my 1973 47' Chris-Craft Commander from the original and completely obsolete Cummins VT8-370Ms to the far more popular 1995 3208TAs at 375hp myself I would suggest sticking with what you have. A repower is far more work than most imagine. I have found the two worst parts were:
1) Modification of the engine beds (Cummins and Cat had very different mounting points both in X and Y). In my case this was a measure 30 times, cut once adventure plus custom fabrication work.
2) The peripheral items that need to be changed to accommodate different engines, like fuel lines, control cables, wiring harnesses, battery cables, raw water, exhaust, propeller shafts, propellers. In my case this took considerably more time and cost than expected.
Parts are still available for 3208s as they built piles of them, especially the 375hp 3208TA. I would guess that was the most popular diesel engine option for production boats 35-45' built from about 1985 to 1995.
I also agree with others, as your boat has a planing hull try to keep the power the same if you do repower. While I run my boats at displacement speeds 95% of the time, I sure enjoy having the get up and go when I need or want it and I believe future owners will as well.
Like you I'm in Toronto and I have had no issues getting parts from eBay (via Crossborder Pickups) or directly from Toromont CAT. If need be, don't be afraid to source large parts from wherever you can get them. My repower was an international affair as my 3208TAs came from Long Island, NY and my ZF gears came from San Diego, CA. My old Cummins went to Guyana and I air freighted a set of transmissions to Gibraltar.
If you get to the point of seriously considering having the existing engines rebuilt by T&S, keep in mind they are only a 10.5hr drive away from Toronto - LTL rates should be reasonable or you can deliver them yourself with a car trailer.