I did a little crunching of numbers.
Amazon says it needs enough space for about 40,000 employees. Tunney's pasture currently houses about 10,000 employees on 49 ha (121 acres).
Tunney's Pasture could be used as a site if it was intensified by a factor of 4x from its current state, which seems very do-able to me.
Using that baseline, these two Hurdman sites make up 50.4 ha so that could also serve 40,000 Amazon employees if it had about 4x the density of the current Tunney's Pasture campus.
This parcel of the Experimental farm could conceivably work as well (close to Carling station and proposed future Carling LRT) but would likely be political suicide for the current federal government. It is 48.4 ha so it would also need about 4x the density of the current Tunney's Pasture site.
Lastly, there's this complex chain of sites in west Centretown/Lebreton. This one would have the best rapid transit and be the most central but only makes up about 27.6 ha. It would need about 7x the density of the current Tunney's pasture campus to make 40,000 employees fit. It'd also probably need a Trillium line station on Lemieux island, renovation of the POW bridge and relocating the water treatment plant.
I think any of those options would be very exciting. The Experimental Farm seems to me like the only option that's not even really worth considering. But I see no reason why the other three couldn't be made into a meritorious bid if we cared enough to do so.