I highly doubt the canary would be a valid defence.
By omitting the line you are, for most intents and purposes, saying that you received a request. Now, saying you received a request and saying specifically what request you received are different, but I imagine the gag order doesn't make that differentiation.
Gag order is not that you can't say a specific thing, it's that you can't communicate a specific piece of information. The canary is communicating something.
A court order can ask you to lie, so the "I can't lie to my customers" defence probably won't work.
By omitting the line you are, for most intents and purposes, saying that you received a request. Now, saying you received a request and saying specifically what request you received are different, but I imagine the gag order doesn't make that differentiation.
Gag order is not that you can't say a specific thing, it's that you can't communicate a specific piece of information. The canary is communicating something.
A court order can ask you to lie, so the "I can't lie to my customers" defence probably won't work.