Canvas relies on your website’s design and content, therefore the time your app takes to fully load is directly related to your website loading speed, plus the time that it takes to load the app’s own assets.
If you are not satisfied with the time that your app takes to load, we suggest that you perform some tests on your website, to make sure it is fully optimized to provide the best possible performance.
The best way to start, would be to use a website speed test tool like Pingdom, which provides some in-depth information about your website performance along with some insights on how you can improve it.
Make sure to go through all the optimization tips provided under the Performance Insights section of Pingdom and you should be able to see some nice improvements in your app loading speed.
Canvas allows you to use any pages from your website inside your app, so you might want to take advantage of this and create specific pages for it, with an app optimized page structure and content.
Synthesizing the content of your app might not only improve the overall user experience but also help with reducing the loading times of your app as there will be less text, images, and code being loaded.