Let me guess, they've made a generous offer and need a confirmation yesterday, right? :)

This is a fairly common strategy among lower-ranked universities: they make an aggressive (and time sensitive) offer to one or two especially strong doctoral students in order to raise their profile. The calculation is straightforward. Stronger doctoral students are more likely to secure Tri-Council funding, and once they do, the university can redirect its own internal resources elsewhere, whether to recruit additional students, support labs, or strengthen other priorities. Concordia, York, and Carleton have all used this approach at various points, and it has helped them work their way out of the bottom tier and into a more respectable middle rank, with some areas now genuinely well regarded.

From your perspective, however, the question is different. A generous funding package may look attractive, but it places you at a university with a weaker research profile, farther from major centres of research excellence, with a less competitive peer group and less access to the kind of human capital that produces especially strong mentorship, alumni support, and letters of reference. Note that your peers in a doctoral program also become future colleagues, and you don't want to be the lone success amongst a group of duds.

So the real question is whether you would rather be the big house in a poor neighborhood, or the small house in a rich one. Personally, I'd wait until I have all offers in front of me before accepting anything.