Go ahead and apply from the USA. From personal experience I know of close friends who were "out of status" in the USA and had no issues with applying to immigrate to Canada.
The issues that will arise are: 1/ did he enter USA legally ... .Answer is Yes. 2/ will he contribute positively to Canadian society .... given he has a work history in the USA (?) , Answer is Yes. 3/ You should provide letters from your family stating both of you can stay with them while he looks for a job in Canada 4/ He should actively seek for a job in Canada while he is in the USA, if he succeeds he'll get a LMO and then you both dont have to worry as he can move to Canada for the job. Tell him to try for a Job in Northern Canada in places like Ft. McMurray, they're paying people $18/hr to pour coffee.
If he is under deportation orders, he should file paperwork to fight the deportation order from the USA so he can stay longer inside the USA and his application is processed faster in Buffalo. In case they call him for interview, and he leaves the USA, his application will be delayed.
Since you have a special situtaion I highly recommend you both spend the money and have a reputable canadian immigration lawyer knowledgable in US law persoanlly assist your application as he/she will possibly guide you best than anyone in this forum. Whatever the price, it will be money well spent.
When it comes time to "Land", travel by car through a western border. The Eastern border Canadian officers are not very nice and cause problems. You should travel to Canada and then return to the USA so you don't overstay.
All the best.