So you have values in an XLSX that correspond to existing email addresses in marketo, yes?
Is that data in a column or field in SFDC or in Marketo already? Ideally, you would have fields in Marketo to drop the XLSX data into, then use the corresponding token to place that in the email:
Dear {{lead.First Name}},
Amount Paid: {{lead.Amount Paid}}
Amount Owed: {{lead.Amount Owed}}
Please pay now.
right?
Now it may be possible to use the API or email scripting to draw the data in from an XLSX, however, this does not sound like an easy thing to do nor desirable. Is there a reason you do not want to import the data to Marketo?
btw, this is a Marketing Activities post.