Well.. here is the point....
Each contact is rated at 20A, however that does NOT mean you should tie them in parallel to get 40A.
Here is the reasoning.
Most of the AMPERAGE value of a switch has to do with life of the switch due to arcing at the contacts as the switch makes or breaks circuit.
However, unless it's your day to win the lottery, no dual pole switch EVER makes or breaks contact on both poles at exactly the same time. When closing, whichever contact makes it home first does the switching, the other just adds reinforcement later. Similarly, when opening, the contact that breaks last does all the switching.
As such, for a brief period one side will be carrying, and worse SWITCHING, the full current. When switching it actually reverts to a single pole switch.
So in effect, though capable of transferring 40A when closed, you can still only switch 20A.
HOWEVER: Your question is confusing. You mention a relay, but seem to be under the impression you need to send the entire load current through the switch. Relay current ratings are for the business end. The coil current is << Relay Rating Current. If for some reason your relay coil current actually IS 40A, which I seriously doubt, buy a better relay.