I disagree - Working for a non Canadian employer doesn't count i believe. Following argument would support it in my opinion.
A US company can employ you any where in the world. As long as you are not physically working in the US, you don't need H1 or any other sort of work permit.
When you are on a closed work permit in Canada, it is tied to the employer you work for IN CANADA. If you are laid off from your job, you can STILL STAY till the expiry of your current work permit IN CANADA although you CANNOT WORK for any other employer in Canada without wp.
As long as the (US) employer can find a legal justified means of paying you - you should be good.
As a side note - many companies in the US employee foreign contracts and pay them via different means. A good example is companies that run free lance sites such as odesk or elance. Similar model can be used i believe.
Still this is just an opinion and besides even if this is true, it would only give you leverage TILL the expiry of current work permit. Work done this way won't be usable towards any immigration program such as CEC.
I think if you declare this to Revenue Authority, they would ask for details and would collect taxes but let you work - else you can stay till the expiry of permit possibly taking Employment insurance without working.