2 part question here.

I'm in Zone 4a/b in Quebec, Canada.

I have a 1 acre flat, south facing lot with fairly heavy clay soil and some drainage issues (some areas can be wet for 3-4+ weeks in spring during thaw and again a couple weeks in fall with rains). Summers are hot (25-35 Celsius - 77-95 F) and fairly dry though with 2-3 days of rain it can be wet for 2-3 days after to drain.

I want to try planting some plums from a couple of local(ish) nursery/orchards who have hardy stock.

I'm getting Toka, Superior, Mont-royal and Kahinta. For 2 of those I have options of either Myrobalan or Mustang for rootstock.

Mustang info I found (http://thehqbooks.com/gb/2036036)

Q1) Anyone able to give me advice between the 2 for my soil?

Q2) Also how would they compare in wet tolerance to Bud 9 for apples? I've got wet and not so wet areas so I'm trying to organize where to place my apples vs the plums this spring - the rootstock that is more tolerant wins the wetter spots.

Thanks.

P.S.

Improving drainage is not an option as I would have to get permissions from over 5 neighbors to trench through their yards.

Planting on large mounds are vetoed by my wife (who is already not super keen on the amount of yard I am expropriating for my mini-orchard).