Welcome to planDisney, Mara!
That's so exciting that you're planning a 
runDisney half-marathon trip in 2027! It sounds like a perfect blend of exercise and enchantment. You've asked some great questions, Mara. Here's the deal:
For runDisney events, the annual "Race Season Calendar" tends to come out in early January of the prior year. General registration often opens around seven to ten months before the event. So for a 2027 event, you should expect registration details to drop sometime in 2026 (likely early in the year), with registration opening later that same year.
Does the half-marathon entry include park admission after the race? Unfortunately, no. The race registration covers your bib, tech shirt, medal, and access to the course (you'll even run through parts of the theme parks), but does not include a full 
theme-park ticket for after the race. If you want to stay and play in the parks afterwards, you'll need to purchase a theme park ticket separately.
Make sure you lock in your travel and lodging early, Mara. Since you'll be travelling from Canada and planning in advance, book your accommodations (ideally at a 
Disney Resort hotel if you can) and keep tabs on the race registration announcement. Having your travel dates flexible around the race window gives you the best shot at snatching up lodging before things fill up.
Happy planning, Mara!
Mike