If you have applied for eTA to Canada you can check its processing at any time. You can find out whether your eTa is active and ready to be used.
If you wish to check your application status please visit status.evisa.express. Please note this applies for those who used our service https://etacanadaonline.com. Otherwise, you would have to go to government's official website: https://onlineservices-servicesenligne.cic.gc.ca/eta/applicationQuery?lang=en
If you have made mistake on your eTA application (for instance wrong passport number or personal information) your details should be appropriately corrected as soon as possible.