Any canned email template you've created can be easily sent to your client from a project. Head to the EMAILS tab of your project and then click on Send Email:
In the composer that pops up at the bottom of your screen, click on the bookmark icon in the toolbar to access your canned emails. Use the search bar to filter through your templates and click on the response you want to send. The email will fill right in... smart fields and all!
You can access your canned emails any time you have an email composer open - just look for the bookmark icon. Use them to send forms, invoices, and even respond back to your clients' replies in the project inbox!