After watching ds9 and voyager how come the borg and dominion never encountered each other? The borgs trans warp hub could reach all four sectors instantly
Apparently, the out-of-universe answer is Paramount was very territorial when it came to using characters/arcs amongst shows. That is a reason why we never saw the Ent-E on DS9 even though Generations to Nemesis is occurring simultaneously. I think even in First Contact they had to change
However, the Defiant class vessels appeared in TNG films and an EP of Voyager "Message in a Bottle".
In-universe explanation could simply be the Borg resided in the DQ and didn't have the interest to break the Dominion in the GQ as they had enemies that could really hurt them at home.