Does the buyer or the seller usually control how the purchase price gets allocated among assets?

Neither side unilaterally controls it — allocation is a negotiated term of the purchase agreement that both parties need to agree on, precisely because it affects both of their tax positions, often in opposite directions. Sellers typically prefer more value allocated to goodwill, which is taxed more favourably as a capital gain, while buyers often prefer more allocated to equipment and other depreciable property, which gives them a higher cost base to claim future depreciation against. Because these preferences pull against each other, allocation tends to be a genuine point of back-and-forth in negotiating the deal, sometimes resolved through a broader trade-off elsewhere in the price or terms.

Whoever has stronger negotiating leverage, or better tax advice going into the discussion, can end up shaping the final number more than the other side, but that's a product of negotiation dynamics, not a legal entitlement either party has to dictate the outcome. Once agreed and written into the purchase agreement, both parties are generally expected to report consistently with that allocation on their own tax filings.

Leaving the allocation vague or unaddressed is worse than negotiating it directly, since an unresolved or inconsistent allocation between the parties' filings is itself a common trigger for a CRA inquiry.