Seattle Expansion question

Yes, if Hyman signs an extension and Toronto doesn't protect him, Seattle can take him and the extension just kicks in for them

I believe, if I remember from last expansion:

if they don't extend him, Seattle can still pick him,
they would have sole negotiating rights with him until free-agency begins
and if he doesn't sign, (this is the part I am uncertain on) he is still unable to sign with Toronto for 1 year

if a UFA is selected like Hyman, they still remain a UFA I think and Seattle wouldn't have their rights. That means that we can still sign them even if they are selected.

true but we may wait to extend him after the draft, with a deal in place but not official

Seattle would hold there rights until the first day of Free Agency. This is 1 week after the Expansion Draft. Seattle would be able to negotiate a new contract before that happens and if they are unable to do so, that player would be a UFA and free to sign wherever.

To the best of my knowledge, pending UFA's need to be protected to 100% guarantee they don't get taken; they are not exempt. Leading up to the expansion draft there is a short period of time where Seattle can negotiate with unprotected pending UFA's. If they can come to a contract agreement in that window, that player becomes their selection from that respective team, if not then obviously they wouldn't waste a pick on someone who's rights they are about to lose.