Well, lots. For example, personally owned assets used in a sole proprietor's business can't just start being used by a corporation. They need to be bought by or transferred into that corporation. For tangible assets like computers and equipment the process is pretty straightforward and can be handled two ways - either sell the assets to the corporation at fair market value or use a Section 85 transfer. If that FMV is the tax cost (undepreciated value) there's no gain or loss.
If the FMV is greater than the tax cost, there will be a capital gain for the sole proprietor. For tangible assets this isn't usually the case because they are usually depreciated as you go along. The problem comes with intangibles like goodwill.
Goodwill, simply described, can be things like the value of your customer list and loyalty. With an established business you likely have a pretty loyal customer base and there is value in that. However, the acquisition cost for that goodwill is often zero, so any value is a gain. To avoid paying tax on this when incorporating, a Section 85 transfer is often used. This defers the taxation until the goodwill is disposed of by the receiving corporation.
Here's where it gets tricky. If you don't value and list the goodwill in your Section 85 transfer, CRA can come along later and assign a value to it. If they do, you will owe tax personally on the gain, but the corporation won't be able to list the acquisition cost for it - effectively resulting in double taxation.
Obviously, there's a lot more to it than I have room to discuss here but the point is that there are many pitfalls that can be avoided by getting, and listening to, good advice when incorporating. Even if you plan on incorporating yourself online, you should consult an experienced practitioner.
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