Short answer: No, you can’t use your Unbounce page for an email campaign template and even if you could that would be a bad idea.
Based on a few years in the email marketing trenches a lifetime ago, I can tell you without a doubt that developing an email marketing template can be a real pain.
There are simply way too many different email clients and email providers. All of them with their own “rules” and quirks.
Outlook being the worst offender of them all.
If you want to support most email clients you are stuck with building a template with HTML from 1999. All CSS has to be inline and at least a dozen other rules.
One of the best features of Unbounce is the ability to position content and elements pretty much anywhere you want. However, that comes with a price - code that works only through Unbounce.
There are plenty of email template builders around that you can use to build your campaigns.
Last time I checked CampaignMonitor had a pretty decent one that allows ypu to export your template and use anywhere you want.