Hopefully not to late to chip in!

I have a shiro plum, santa rosa plum, and french plum but not sure I can be very helpful with what is more resistant to canker.

But I find that out of these 3 Shiro is the most vigorous and disease resistant, the french plum grows fairly well not much disease problems but also not as vigorous, and the Santa Rosa always has some kind of leaf spot, brown rot, or other stuff, but continues to live and grow but least vigorous of the 3. I have had 2 problems with borers on the Shiro but caught it quick and killed them with the wire method.

Also the Shiro had a fairly large injury that you could see the heartwood (innermost wood part) after something took a bite out of it. But I was constantly putting powdered sulphur as a fungicide (I dust all plant injuries with it) to help prevent infection since I was afraid of canker, who knows if it truly helped, but 2 years later the wound has completely healed and did not get infected. Perfectly healthy right now.

My spray schedule is basically: late winter before bud break dormant oil for overwintering pests, 1-2 week later daconil fungicide, Petal fall daconil + sevin, sevin on first cover (seven days), sevin again at about 2 weeks. Also, if weather is abnormally wet I will do another application of daconil or other fungicide. If pests a problem later in the season sevin is fine. Depending on how the trees do I will sometimes do another fungicide in the fall after leaves fall and are raked up.

Seems a lot of spraying but when it's spread out its not too bad and it really depends what diseases/pests in your area. And I have a lot of flowers and bees in my yard and they are fine, they stay away from trees at petal fall when the flowers are gone and for extra safety stuff can be applied in the evening when bees are gone.

This is the spray schedule I started off with at first, but after a while you can tweak it and change products and timings once you know your environment well and how trees respond: