You mean antarctic bird
Disclosure:
Ok, here goes. I've done BR since that AC culture thread around 10 (or 12, I lost count) in J and did PE on BR (or Elite Class) twice TPAC as a kid. So my memory is fading a bit, although I did join a colleague in Elite class a few weeks ago for a few hours of...pong. So full and fair disclosure, while my BR memories in elite class = decent, my PE memory on AC = not existent. I can only comment on AC PE for its hard product and "service" (domestically), but not its food internationally, for sure.
Firstly, general comments and then i'll get into upgrades.
If BR was cheaper, I'd fly BR (with a few points against it which i'll talk about later). Since the AC PE flight is cheaper, then with the COS upgrade is something to look at. Elite class on BR books into K/L/T with K/L giving you 115% and T giving you 100% while AC PE gives you 125%. So if qualifying miles is something you're looking at, book AC PE.
I physically find that the AC PE seat on the 787 (the only one I've been on, I have not been on the 777HD) to be SLIGHTLY superior to the Elite class (AVOD being the main diff. BR's IFE blows). I will not comment on the HD seat as I haven't been on it, although FT will tell you that the seats are hard. The Elite class seat did not strike me as "hard", it just struck me as... "a seat". I'd say legroom and shoulder room are pretty much a wash on both. Potatoes potaaatoes. Some of the seats in Elite are getting pretty old though, and that TPE YVR flight from what I remember is on a 744 - which, while infinitely cleaner than AC, is still getting long in the tooth. (I have flown the 744 on BR, just not that route). If you put a gun to my head, ok, I'd say the AC PE seat is better on the 788 than the Elite seat (when I flew the 777). Then again, not the same bird...so...grain of salt.
As far as the soft product goes, I can say that the Elite class food is ok, nothing crazy to write home about -had dinner with a colleague in Elite and forwent my J meal. The service is hit and miss. I got my glass refilled a lot quicker in J than while playing my favorite new game introduced by the cow in Elite. The service isn't as warm in Elite, but I still think its miles ahead of AC (unless you have an awesome crew on AC).
So in conclusion before I talk about upgrades, if Elite was cheaper than AC, I'd book Elite with BR. If PE on AC is cheaper, I'd save your money and get 125% miles instead.
Definite downsides on BR: The cabins are pretty warm. 23'C to 24'C. TOO hot for me. As I have mentioned in the past, to get around this, wear thin clothes, and buy a USB fan on Amazon for like $10. Keep a glass of ice at your chair, keep one hand on the ice, keep the other with your favorite drink.
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Now, if you have the ability to upgrade, all bets are out the door. I would not be booking elite on BR in the first place, although as Stranger mentions, you could upgrade from Elite to J. (HOWEVER, not all fares allow you to do so). The only fares that will allow you to upgrade from Y/Elite to J are K/Y/B fares. Not all elite fares are upgradable, and not all fares in economy are upgradable. From what I remember, the cheapest fare in economy is not upgradable as it doesn't fit into those 3 fare classes. I don't recall the naming on EVA, but the Tango equivalent is not upgradable, but the Flex equivalent is. So - not economy (dirt cheap class), but economy (sort of cheap class, but not the cheapest class) books into a B (IIRC). Then TWO weeks out, J inventory usually opens, and then you can upgrade. I've dummy booked 8 seats before, and have had numerous colleagues actually book 6-8 in total two weeks out - so totally do-able. Sure, you don't get the COS, but whatever, it's still 100% miles.
J on the 744 from YVR is nothing to write home about. The hard product is dated, but the food is a 8/10 in general (e.g. good/great, but not jaw dropping) (or 6/10 to 7/10 compared to CX F). My colleagues and Mrs. SAP were fond of the burger, but not the rest of the Western meals. The Asian meals are where it's at (duh, it is a Taiwanese airline).
I would not be booking Elite, and then hoping for an upgrade. You'd be paying MORE and playing Evalotto. In this case, I'd either book economy that will book into Y/B (K I believe is the class you need for elite), and play Evalotto, or just save yourself the grief and fly AC PE.
The decision is clear as mud because Eva is not the cheaper option in this case.
OR...if you can, get yourself to a place that flies the 777 (SEA? - just going from a distant recollection on FT) and book yourself into Royal Laurel J.....mmm.
As far as FA's go. If you speak English - it's OK. If you speak Mandarin, it's WOW. From a FA to Pax ratio, EVA is FAR FAR superior. From an eye candy perspective, hit and miss on AC, more hit than miss on BR....
My colleagues were really worried about drink selection on BR...umm, not to worry. Everything (At least I wanted to drink) was plentiful on BR....and they do NOT cut you off. (at least none of us did..., and we would have been beaten by AC FA's for our....indulgences....)
EDIT: If vernonc's comment is right, and the OP is booking NRT - YYZ...wait - YYZ? Anyways, if it is then IIRC that's on the 788. So then my smorgasbord of experience above can help. As I mentioned above, if the OP ends up flying the HD, I have not sat in any seat on that bird, and I hope I never ever do!