CRA states that an unpaid GST/HST remittance obligation can be offset against an ITC if the vendor and purchaser amalgamate
If A is assessed for failure to charge GST/HST to B, and then amalgamate, Amalco may generally claim an input tax credit for the GST/HST that was payable by one predecessor to the other (so that only interest is now payable on the assessment). In particular, Amalco can issue an invoice on behalf of one of its predecessors containing the required GST/HST particulars, so that Amalco in its capacity of successor to the other predecessor can satisfy the documentary requirements for claiming an ITC.
Neal Armstrong. Summary of 23 March 2017 CBA Commodity Taxes Roundtable, Q.11(b) under ETA s. 271.