I generally consider 2 volumes of CO2 to be towards the very high end for British styles, which is what 2.75 oz of cane sugar would give you. I would, more usually, limit it to 1.5-1.8 volumes, which would be 1.5-2.3 oz in 5 gallons. Just be aware that that is a somewhat subtle level of carbonation and might seem flat to someone used to US bottled beer.
I use a tap-a-draft as well. If you leave a beer with a low level of carbonation on the tap-a-draft, it will continue to absorb CO2 due to the pressure used (when the canisters are full) and gradually become more carb'ed over the course of a week or two. If you are drinking the beer, the pressure will drop after a few pints or so and that shouldn't be an issue.