score:3
After a week in Paris, I came to the UK via the EuroStar. As a Canadian citizen, the passport machine let me in. No questions asked. Phew!
Upvote:2
No one can accurately predict what will happen during your landing interview. You’re potentially a bigger flight risk because you've clearly built up a life in the UK; on the other hand what you are proposing is not against UK Immigration Rules https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules and your citizenship is probably a point in your favour.
In comments you gave some possible reasons for your wish to return. Having a legitimate premise to show you are a genuine visitor and being able to articulate it convincingly is important. Presumably you can prove sufficient funds and will stay with your partner, so your accommodation is sorted, and you already have your flight back to Canada booked.
The usual advice in these situations is ‘if in doubt, get a visa’. Clearly this isn’t possible in your case since your planned return date to Canada is so close. Overall, although there’s always a risk that you could be denied entry, it is probably a small one. The 100% safe choice given your postdoc plan would be to fly home to Canada from France.