Which lens may be best
Canon EF 100-400mm F/4.5-5.6 L IS USM Len
Nikon AF 200-500mm F/5.6 AF-S
Sigma 150-600mm OS lens (Canon EF fit) F/5-6.3
The Canon is better for Light but gives 400mm
The Sigma not as good on Light but gives 600mm
Are Sigma lenses good and reliable?
Does the lens fit direct onto a standard tripod or do they need an adaptor?
Well we can take the Nikon off the list as it doesn't come in a Canon mount
Next lets talk superzooms
First up lets actually talk production. All the camera products are produced in batches and produced within tolerances of manufacture and tested in batched groups (higher priced lenses get more individual attention in general but are still produced within tolerances). These tolerances, in general, work for the most part, you might get some very minor variations, but those are invisible except if you test a wide range of gear side by side and start comparing at high magnifications. Ergo its a null issue.
Now it is possible to get a camera and lens which have their calibration at the opposite ends of the tolerance scales - this can result in reduced performance because both are totally out of sync with the other. Neither is damaged, broken or badly made, but they are at opposite ends. Thus if you sent one in for a warranty repair, it might come back better or worse because the techs would only be adjusting its calibration, and if it wasn't really out to start with any adjustment could nudge it further away from the cameras own setting. That's why you often have to send camera and lens in at the same time.
And because things are produced in batches its likely that if you got a replacement copy from the same store you'd likely get another from the same batch and possible with the same/similar calibration.
Let me repeat that broadly speaking the chances of this happening with most lenses (even most 3rd party) is small for the most part.
Now back to superzooms (like the 100-400mm) - these are complex and their tolerances are often a little broader. Thus there is an increased chance of getting one out of sync with any camera. Indeed the original 100-400mm was well known to be a lens where if you got a "good copy" it was great, but if you got a "bad copy" it was rather poor. And, because of the ways calibration is done as outlined above, it could be that people would get copy after copy or repair after repair and get no improvement (because each time it was lens only not with the camera).
They can also show variation in focusing through their focal range as well - since most focusing is done via AF rather than manual focusing with digital cameras.
Now more modern cameras are starting to get features built in for AF correction and newer sigma lenses even come with a dockingstation base (lens cap with a USB slot) to let you adjust the lens AF software (far cheaper than sending it in to be repaired and future proofs the camera as rarely very old 3rd party lenses have to re-chipped to keep up with changes in own brand).
Now lets fast forward to the last few years; in the last few years Sigma and Tamron have both released some rather impressive superzooms (I forget their names though I'm sure others can fill you in) and Canon has released a newer 100-400mm MII - in these newer lenses the performance and reliability is greatly improved. Granted the costs are greater, but the performance is far better.
Honestly were I in your situation I'd consider the 400mm f5.6 or the newer Canon 100-400mm MII - those would be the best choices for performance and whilst they might take longer to save for, I think that the cost would be well worth the investment - esp since both would give you good enough performance to also crop shots by a decent amount; which isn't cheating, esp if you are not able to get closer (many reserves your position is fixed in a hide - even if you're fully able many wildlife require a static hidden/concealed/distant position to get the shots so moving closer is often not possible - thus cropping is oft used).
Of course the 3rd party newer superzooms do give you more reach - so that's a big area to research, though I think if you start a new thread asking about those you should get some feedback from users.