well matthews' salary is 13.25.If he stays in Toronto he's not getting more than Matthews so there's a hard cap at $13.5AAV there. let's assume it's $12.5-13 x 8. I think this is the most likely option.
If he leaves Toronto then he's just gonna go max money with an NMC. A team would be crazy to pay more than Draisaitl @ $14m AAV but maybe someone is desperate enough to do that but he's clearly not better than Leon and he's also not a C but he is like 1.5 years younger so you are getting more 'prime years' I suppose.
If he doesn't work out in Toronto, I gotta think he wants to go to a contender since he hasn't won anything at the NHL level or come even remotely close. This next contract is gonna determine the course of his career so it would be odd to go to a rebuilding team just based on the hope that they could be competitive one day. But also who knows, maybe he just wants the biggest bag possible and that's fine too.
IMO i think the MINIMUM he would accept from toronto is 13.5x8. be shocked if he took any less.