CRA requires a minimum of 50% margin as security for exit tax (and resists partial pledges)

In the situation where an individual leaving Canada wishes to post security with CRA for the exit tax that otherwise would be payable on the deemed disposition of the individual's Class A and B shares of a CCPC, CRA will require that the shares of both classes be posted as security - unless for some reason it is possible to furnish only shares of one of the classes, in which case CRA will accept the shares of the one class if their value is at least twice that of the exit tax.

Neal Armstrong.  Summary of  5 October 2012 APFF Round Table, 2012-0454231C6 F under s. 220(4.5).