TLDR; I can't decide whether to just stick with United MileagePlus or split my miles between AirCanada and United - I "could" travel 25k - 50k miles on AirCanada and around 50k-75k on United. I wouldn't mind getting bumped to Biz Class on my AirCanada flights but I'm at a loss whether splitting programs is a bad idea.

1. What is most important to you in a frequent flyer program (FFP)?
Upgrades for AirCanada, Good Award Redemption for United


2. How many miles do you usually fly each year? How many flights/sectors?
(e.g., <25000, 25000-50000, >50000 miles and <25, 25-50, >50 flights?)
25k to 50k on AirCanada, 50k - 75k "likely" on United, 8 - 12 flights on AC, 24 - 40 on United

3. What fare class do you usually buy?
(e.g., first, business, premium economy, economy)

Economy

4. Are you able to choose your airlines and/or class of service? Do you travel for work and/or pleasure?

Mostly work

5. Which routes do you fly most often
(e.g., U.S. domestic, transatlantic, intra-Asia)
US coast to coast or US to Canada

6. What is your home airport?
(e.g., SFO, LHR, HKG)
SFO (I fly a lot to BOS and YOW/YYZ)

7. Do you have status in any FFP? What is it? How miles do you have banked in a FFP, if any?
16k on AirCanada, 24.9k on United

8. What are your preferred airlines, if any?
AirCanada and United