The maxcap for a canbomb is 7000 power. The canister ruptures at 145908kpa and beyond, and gains a three percent chance to rupture at 127669.5 kpa. The min pressure for the canister to boom is 7000kPa and the min temp is 100000K. Just fill the plasma tank you attach the canister to at 1013.25kPa with plasma. The mathematically ideal safe mix is 127669 kPa and 1.86556e+09 Kelvin, but lower pressure is usually preferable. There's higher but risking the 3% chance for a few extra decimals of power isn't worth it. Also to note: You can use any gasmix for the canister.

If you wish to use oxygen, beware that it is worth 1/6 of plasma. The ideal mix for only explosions is 673.16K Kelvin and 100% (1013.25kPa) plasma. If you want for some fire too then go 673.15 Kelvin or below, as it'll remove all devastation heavy damage, dump its contents to the ground, and weaken the explosion. At 523.15 Kelvin and below, the explosion will be weakened even further. And at 373.15 and below, no explosion will happen. It will merely dump its contents.