Not quite sure what you mean by NIC, but if you're refering to something like an external router and it has a power adapter with a round plug that goes into the router, you can just buy a UK power adapter with multiple DC outputs and plug in the one that's suitable.
I'm guessing Canada use ~110V mains? Alternitively, you could get a power transformer to step down the voltage from 230V to 110V and plug straight into that. You could also use one for your PC, but you have to check the power rating is sufficient and the higher power converters can be expensive, so it might be as cheap to swap the PSU.
If your monitor is fed with electricity from your computer and you've got a voltage selctor switch on your PC then you should be okay. If the monitor has its own mains plug, going directly into the wall socket, then you need to check if there is a voltage selector on the back of the monitor. Otherwise you will need a stepdown transformer for it.
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