Are those devices allowed on a flight which create their own WiFi signals? I am going from Canada to Mexico but I don't want to be dependent on in-flight entertainment. Thus I got seagate wireless plus so I can stream to my iPad. I couldn't find any policies I can use this device during flight or not. At very least I am trying to determine if it is worth asking the flight company?
No, the rules are about any transmitter or receiver, regardless of whether it comes under the specific category of phone/tablet/laptop etc

If anything your device is worse as it transmits at a higher power and range than a receiver.