Do I copper - pour on mains voltage PCB?
First, thicken up the power traces to make absolutely sure that (if life gets interesting) fuses will blow or breakers will pop rather than your PCB traces vapourising. In my opinion a 0.25 inch track width is not too much.

Second, space out the traces to get at least 0.25" between live and neutral, and a bit more (0.5" if you can) between either and any other circuitry. This is an ideal; if a component forces less clearance, do what you have to do.

And I would prefer a bit more clearance rather than copper pour. But if the board is huge, I would consider a copper pour in areas more than 0.5 or 1 inch from mains circuitry.

There is no justification for such large clearances in the PCB materials themselves; I have seen guidelines that say 5mm is adequate. But as boards age, there may be contaminants... I have seen one board that would have survived longer if its live to signal clearances had been bigger than a large (carbonised) ant!