Having said that, to a certain extent "artistic license" is the order of the day. The real ships wore a dizzying range of variations on published schemes; I've seen RCN orders auth commanders to make their own adjustments, so ultimately it is nearly impossible to know for sure.
If it's a two colour scheme on white background, I'd probably go with G20 on the hull and G45 on the superstructure; these two colours compliment each other and look "right" together. The G45 I have is from Soverign's old WEM line and does have a very slight green tint to it, but it's definitely a light grey. The new formula for G45 from Sovereign I'm led to believe is much more grey. Note that Sovereign has also reformulated the G20 and is much greyer then the previous very(nearly black) dark green. I would also add that B30 is a very pleasant colour that to my eye also compliments the G20 rather well, so that's another option. I have found some Vallejo colours that match G20 and B30 fairly well, just don't have the numbers in front of me.
Deck colour is another wild card. RCN very generally used grey, but even where other colours were used the effects of wear and weathering quickly changed those to a mix of......whatever. For uniformity and simplicity I generally use a dark grey (Tamiya XF-53 is my go-too) for all RCN decks. These are just my opinions based on research (mainly by others!) availability of paint (Soverign is very hard to get in Canada) and my personal "artistic" opinion. I hope this is helpful!