If you're on a cellular connection at the time, cellular data. As for the amount of data, that would depend on a number of factors including speed of connection (ie 3G vs LTE/4G), the quality of the video (480p, 720p, 1080p, higher if they make it available), and your phone. Data usage is estimated to be up to 900MB-1GB per hour for a high quality stream. Crave's website says one thing about data use and all the telecoms say different.
Crave (possibly web only but may apply to cellular) - source: https://www.crave.ca/help-and-frequently-asked-questions-74295754
How much data does Crave use playing video?
On Crave.ca, users can control the quality of their video playback. In the video player, click on the gear icon in the bottom right corner. Users can select from a list of video playback options with 720p being the best quality available. An hour of 720p playback will use approximately 2.5GB of data.
Approximate amount of data used per bitrate:
The Crave apps use a video player with an adaptive bitrate and the apps will always auto select the highest bitrate available based on a user’s network speed. To control your mobile data usage, go to ‘Settings’ and turn on the ‘Stream only on Wifi’ option. This will limit playback to devices connected to a Wifi network.
On your Optik TV set top box:
Viewing Crave TV using your Optik TV set-top does not consume data.
On your TV or computer:
Streaming video will use between 0.2 and 0.9 GB per hour of viewing. Whether or not this will result in additional charges depends on:
On a mobile device:
If you are connected via Wi-Fi, using the Crave app on your mobile device will not count against your cellular data plan. If you stream content using data, however, then it will count towards your cellular data plan even if you are connected via Wi-Fi.