I don't see why you'd need more than one TRIAC unless it's three phase or split phase.
The TRIAC will heat up, there's no way of avoiding that.
I don't see how using two TRIACs in parallel could possibly help unless you use two opto-couplers and even then they wouldn't current share very well. With one opto-coupler, the fastest TRIAC will just fire, leaving the other one redundant.
Using zero crossing (MOC3041) and a snubber network will give the TRIAC and easier life but it will still need to use the same amount of heat.
Is it possible to use the fluid being pumped as a cooling medium?
If it's a copper or brass pipe you could mount it to a metal plate joined to the pipe (with a suitable insulator and earthing of the pipe) which should act as a very good heat sink.
How much current does the pump need?
What about just using a relay?