These trucks don't have the greatest airflow to the radiator (and intercooler, if your truck has one) at the best of times, so adding something that would potentially reduce that airflow further may prove problematic.
I don't know how your truck is configured (upgraded front bar, recovery winch, different seats, sound deadening etc.), but another thing to take into consideration is that you would need to ensure you do not exceed the maximum load rating of the front axle, as there is not a lot of wiggle room in that area with the Canter.
If you have super singles on your truck, then there is the issue of how you will lift the spare wheel up onto its mounting bracket, given that these wheels are not what I would call lite.
And finally... if you intend to tilt the cab, you will probably have to design the spare wheel mounting bracket to tilt as well.