From
www.qp.alberta.ca/documents/Regs/2002_304.pdf
(I can't get the PDF to open.)
2(1) A person shall not do any of the following:
drive a vehicle at such a slow rate of speed so as to impede or block the normal and reasonable movement of traffic then existing on a highway except when it is necessary to do so for the safe operation of the vehicle or to comply with Parts 1 and 2.
Bottom line, let the police do the policing of traffic laws.