The proposed office tower at Luxe on No. 3 Rd. in Richmond by Townline and Canderel is probably more than 25,000 sq ft.
https://www.mikestewart.ca/presale/luxe-...presale-condos-by-townline-and-canderel/
Likewise, the Bridgeport Business Centre tower (Phase 1) in Richmond completed last year is 231,279 sq. ft.
- but it's not quite in a "downtown".
https://www.scottconstructiongroup.com/our-projects/bridgeport-business-centre-phase-1/
There's also the First West Credit Union Building in Langley at 130,000 sq ft near Hwy1 and 200th St. but it may be a few years old.
https://www.loopnet.ca/Listing/19933-88th-Ave-Langley-Twp-BC/17256603/