re: Quebec...
Clark was the guy who talked about Canada as a "community of communities", a concept which had some resonance with the soft-nationalist elements in Quebec(cynical take on that: the Alberta community gets to drag peasoupers behind pickup trucks, the Quebec community gets to beat anglophones with baseball bats, with no federal interference in sight).
So, unlike Diefenbaker, Clark did actually have a vision of Quebec-within-Canada with which he could approach the Quebec electorate during a referendum. Problem is, if his majority doesn't include a contingent of highly respected figures from Quebec, he's severely handicapped in terms of being able to sell it to the public there. What impact this has on the referendum, I don't know.
It is a little ironic that Clark's view of federalism was probably closer to what was then emerging as the consensus in Quebec(as exemplified by le beau risque a few years later) than was Trudeau, but Trudeau at that point still had more cultural savvy in the province to sell national-unity.
re: the Constitution...
I don't see Clark doing anything, besides maybe just a simple repatriation, and even that, probably only as a bone to anti-imperial sentiment in Quebec during the referendum. Any talk of a Charter Of Rights would outrage his redneck base in western Canada, and be looked on warily by almost everyone who mattered in Quebec, unless it contained some proto-Meech style deference to Quebec as a unique province.
Heck, even without Quebec weighing in, it would only take about one meeting with Alberta backbenchers screaming about "goddam gay French turban criminal rights" for Clark to put the kibosh on any plans for implementing a Charter.