The old BR9EV were the top of the line plugs from NGK.....They used a fine wire center electrode (gold Palladium, maybe?) that was extremely durable, and by it's design, resisted fouling better than standard plugs.
Several years ago, all of the spark plug manufacturers started using iridium for the center electrodes in their premium plugs....iridium is even better then gold palladium.
The NGK BR9EIX (iridium) is a perfect replacement for the BR9EV.
The iridium plugs cost a bunch....I know you are in Canada, but the BR9EIX cost about $11 each in US dollars.
2 other NGK plugs will work great:
BR9ES.....pretty much a standard plug....only about $2.50 US
BR9EYA....similar to BR9ES but a V-groove added to the center electrode, which helps resist fouling a bit more than the standard plug.....cost about $3.00 US,
The iridium plugs are no doubt the "Premium" plug....In a car or truck you can install them and expect them to last 80,000 miles because the center electrode is nearly as hard as a diamond.
Are they worth it in sleds??? Only you can decide. I change plugs in my sleds often enough that electrode wear is never a concern.
Both the BR9ES and the BR9EYA when new will perform exactly as well as the BR9EIX, I believe.....a spark is a spark.
Will the iridium plug last longer and resist fouling better?.....yeah, probably.
4 out of 5 of my sleds use this plug...I have used the BR9EYA plugs for awhile now, and they work great.
If I buy a box of 10 of the iridium plugs, I almost have to go to a bank and take out a loan.