It's true, we don't know if they want to resign him, or whether he would even want to resign when at his age, he's probably looking at 1 free agent contact in his career. Lots of players find that a hard thing not to test out especially when you're a great player.
However one can reasonably speculate what the management is leaning towards, given their track record from their previous team.
My speculation is that the only way they resign Donaldson is if the Jays are:
1) in very good spot for a playoff position by the all star break.
And then , only if #1 is true
2) Donaldson is willing to sign an extension in the 4 year/100 million range before the trade deadline this year.
And then only if #2 is true
3) they really feel strongly about another playoff run in 2018
#2 wouldn't even come into consideration if the Jays are way out of a spot because at that point Donaldson will be at his highest value to any team trading for him because they would get at least 2 potential playoff runs with him before free agency. There no logical reason to keep Donaldson for 2018 if you aren't making the playoffs this year and he's your best trade chip to kickstart the inevitable rebuild.
Yes, he would still have value before the start of next season, and yes he would still have value at next year's deadline, but it's inarguable that his highest value would be at this years deadline assuming he is healthy.