two circuits into one jb ?

I live in Ontario and would like to know if it is ok by the Ontario Code to bring more than one circuit into the same electrical junction box. The situation is that I have added pot lights to a room that has an existing ceiling light, but because there are already almost 12 devices on the first ceiling light circuit, I need a new circuit for the pot lights.
I want to have a double gang light switch with one for the existing ceiling light and another for the new pot lights, but these are from different circuits. I know I obviously can't tie the neutrals or black wires together, but am concerned as to whether it is acceptable by code for two circuits in the one (double) box. I cant find reference to this in the simplified Ontario Code, and would appreciate any guidance. Thanks.