Yes, it can be. The post-purchase transition period where you stay in the business needs to be a clause in the Sale & Purchase Agreement (SPA). Both you and the buyer need to agree the terms before the SPA is finalised.
The standard handover period in the Standard REINZ/ADLS Sale & Purchase Agreement for a Business is two weeks, full time, and your time and costs for this two-week period are included in the purchase price for the business. If the buyer wants you for three months, you need to do some more negotiation. If the buyer wants you to work in the business, or even just be available to answer questions, after the two-week transition period then you should be paid for your time, and you’ll both need to agree the rate before the deal closes. Further, the buyer can only expect you to carry on doing what you were doing before they bought the business – you don’t have to do menial tasks or things you are not skilled or able to do.
It’s essential to also clearly define the terms of this arrangement, such as your specific responsibilities, working hours, and extent of authority. These details can be part of the overall Sale and Purchase Agreement, or a separate contractor agreement.
This topic is also discussed in Transitioning Out of Your Business.