I recommend you use the standard REINZ/ADLS Agreement for Sale and Purchase of a Business. This is a complete agreement in most cases, and pretty much every lawyer is familiar with it. If no broker is involved, your lawyer can provide this and also assist with any custom or special clauses. This is a copyright-protected and licenced document, so there will be a fee to use it, which your lawyer will charge.
Don’t use a bespoke agreement drafted by your or the buyer’s lawyer. This adds significant cost to both parties.