Terminated and contracting back.

I haven't seen this one posted, so here it is:
I work for a Canadian subsidiary of a large US coporation. In 2009 the plant I worked at closed. After several options were considered I stayed on in Canada for 2 years working for the US plants from home but still paid through the Canadian subsidiary. Most of what I do I can do remotely, but I got an L1B visa (specialized knowledge) for the trips south (numerous, but < 183 days).
At year end I reach the end of that agreement and will be terminated with 2 years severance, which will get me to my pension. The company and I are interested in continuing my work with them (pretty much full time) through a third party (basically a US based talent agency) under contract, which is how they hire back retirees (mostly US retirees). I turn in time sheets/expenses and an invoice to the agency, they pay me, and in turn invoice the corporation - their client.
I expect my L1B becomes void as soon as I'm terminated.
I will still need to visit the plants in the US periodically - perhaps often (< 183 days) - for meetings and to provide instruction and advice on the process control systems the US plants have that I am an expert in. I don't have a degree.
Will I need a visa? What kind? And what are the tax implications of being paid by the US agency?