There is a difference between US and Canada on this one--the FAA TERPS says that the MSA is for "emergency use only", it is not an operational altitude. One reason, in the US the MSA is not surveyed for signal coverage, nor does it guarantee it. Also, from a US Terpster, the MSA is not resurveyed unless there is a change in the basic procedure, hence, there is a possibility that an unsurveyed may exist in the off-route areas.
That is one reason why US ATCOs give the approach clearance with specific altitude instructions. Well, one of the reasons, those ATC instructions all came from the TW 514 accident.
That is US only, other countries have other ways of applying the MSA.
GF
Thanks for the correction! I didn't realize that.