Can I still qualify for the capital gains exemption if I've been renting my business premises to my own corporation?

Quite possibly, and this fact pattern is actually treated differently than a corporation renting out excess space to strangers. If you personally own the premises and lease them to your own operating corporation, that real estate is your personal asset, not an asset sitting on the corporation's own books, so it isn't directly part of what the qualification tests measure when looking at the corporation's shares. Many owners deliberately keep real estate outside the operating company for exactly this reason — it helps keep the company's own asset mix cleanly focused on active business assets.

What does matter is whether the real estate itself is being sold as part of the same transaction. The exemption applies to qualifying shares, not directly to real estate you hold personally, so if you're also selling the building, that's a separate asset with its own tax treatment, calculated on its own terms rather than sheltered by the exemption that applies to your corporation's shares.

Because the exact structure — who owns the building, how the lease was priced, and whether it's being sold alongside the business — all affects the analysis, having a tax advisor review your specific ownership arrangement gives you a clear answer rather than a general assumption either way.