Aside from the currently irrelevant but historically awesome Cubs/Cards and uninspiring Yanks/Red Sox: the MLB really lacks meaningful rivalries. It's time for realignment.
My suggestion:
Guardians from the AL Central to NL Central. Cleveland/Cincinnati is a natural regional rivalry.
Pirates from the NL Central to NL East. Pittsburgh/Philly is also rivalry that makes sense.
Marlins from NL East to AL East. Still, no one will care, but Miami/Tampa.
Finally, completing the circle, the Jays from the AL East to the AL Central where god intended, to selfishly reestablish the Jays/Tigers rivalry that consumed young Jer circa '86, '87, '88.
That is all.