That tree has three or four trunks. Perhaps it was a grafted tree and the roots sprouted a few more trunks. Did one trunk have the good fruit? It might just be a pit that was planted, a seedling from a 'good' plum. Without seeing the fruit we can only speculate.

A description of the fruit, color, size, taste may help in identifying it. But I suspect that you won't be able to find an exact replacement tree. Good luck....

OK, I did a little research for you. I suspect that it could be an American plum, (Prunus americana); it could also have been a Canadian plum, (Prunus nigra), or even a hybrid of the two. Was the fruit yellow or reddish to purple, (some American plums are red, some yellow and some any color in between and beyond). These plums also tend to sucker and form a multi-stemmed tree. Did the tree have any thorns, small or large? This will help identify it for you.

Need a picture of the fruit.

Thanks everyone for your replies. Unfortunately I don't have a photo of the fruit. The last few years it did develop a fungus (which I think is called plum pocket). You can see a withered plum in the second picture.
Before that though, the fruit was always good and sweet.
theaceofspades: you may be right about it being planted from a pit. That sounds like something that my grandfather, whose property it was, would have done.
destin_gardener: It didn't have any thorns. From my online reading, I think that yes, it is likely a Canada or American plum. It was really a hearty tree for being so far north, so I think a native tree is probably a good guess.
Thanks again. And if anyone has an idea, please chime in!

It's going to be impossible to identify with just a photo of the tree and blooms.

I suggest that you ask about what is the best growing and tastiest plum for you growing conditions and get one of those trees.

I'd say the contractor owes you more than a small replacement tree. Mature trees have some real value.