Ecommerce site with .CA AND .COM best way to redirect based on Geolocation without affecting SEO.

Today, we had a huge drop in rankings, and among the edits we made was adding a new entry screen where users can select CA or USA depending on their location. Now, could this negatively impact our SEO?

What's the best way for an eCommerce store with a .CA site and a .COM site to redirect their users based on their location without any negative impacts on SEO rankings or our SEO efforts?

Additional edits/issues:
- [issue]Homepage redirecting to the shop page (probably 90% of the problem here)
- [edits]Speed optimization (unsure of this, some coding was cleaned up)