You mean every legendary currently in existance, correct?
That's unlikely, but from what I know, these legendaries are going to make the cut:
Legendary Dogs
Lugia
Ho-oh
Groudon
Kyogre
Rayquaza
Arceus
Possibilities:
Mewtwo
Celebi (event-only, probably)
I highly doubt any legendaries that appeared in D/P/Pt will appear in HG/SS. For the record, the Legendary Birds appeared in Platinum, which is why I didn't list them.
.