Hey Stan, just let me know when, and I'll arrange some fishing for you
Depending on when exactly you plan to be here, you could be looking at small stream fishing for brook trout and brown trout, small river fishing for steelhead, pike and walleye in the lakes, whitefish in the lakes as well, some great perch fishing...and it goes on and on...heck, maybe even some trolling in the Great Lakes.
Generally, trout season opens at the last Saturday of April, pike and walleye opens the 2nd Saturday of May, and I think whitefish and lake trout opens the 2nd Saturday of May as well on Lake Simcoe. Most places that I fish in May are within 1-2 hours drive away.

Unfortunately, muskies won't open until 1st Saturday of June.
I'd say in terms of consistency, perch and whitefish is most consistent, then comes pike (and maybe walleye), small stream trout may be okay (but I usually don't fish small stream until early summer...so I would have no clue what is hatching in May). Musky could be hit or miss...and come 3rd weekend of May, most of the steelheads has left the rivers and returned to the lakes.
I don't have a boat...but I know enough friends who do...and they're all friendly and willing to show a visitor a great time, with some great Canadian hospitality
The only difficult time would perhaps be April 10th-30th. I may have a conference to go to between April 12-16th in San Diego...and I may visit my aunt in Long Beach after for maybe a week (plus a day on a party boat fishing

) Nothing is sure yet...but I am submitting an abstract to attend the conference.