You can add the report template by mail.template model with the attribute
<field name="report_template" ref="modulename.report_name"/>
eg:
<record id="email_template_edi_invoice" model="mail.template">
<field name="name">Invoice - Send by Email (Portal)</field>
<field name="email_from">${(object.user_id.email and '%s <%s>' % (object.user_id.name, object.user_id.email) or '')|safe}</field>
<field name="subject">${object.company_id.name} Invoice (Ref ${object.number or 'n/a' })</field>
<field name="partner_to">${object.partner_id.id}</field>
<field name="model_id" ref="account.model_account_invoice"/>
<field name="auto_delete" eval="True"/>
<field name="report_template" ref="account.account_invoices"/>
<field name="report_name">Invoice_${(object.number or '').replace('/','_')}_${object.state == 'draft' and 'draft' or ''}</field>
<field name="lang">${object.partner_id.lang}</field>
<field name="body_html"><![CDATA[
<div style="font-family: 'Lucida Grande', Ubuntu, Arial, Verdana, sans-serif; font-size: 12px; color: rgb(34, 34, 34); background-color: rgb(255, 255, 255); ">
<p>Hello ${object.partner_id.name},</p>
<p>A new invoice is available for you: </p>
<p style="border-left: 1px solid #8e0000; margin-left: 30px;">
<strong>REFERENCES</strong><br />
Invoice number: <strong>${object.number}</strong><br />
Invoice total: <strong>${object.amount_total} ${object.currency_id.name}</strong><br />
Invoice date: ${object.date_invoice}<br />
% if object.origin:
Order reference: ${object.origin}<br />
% endif
% if object.user_id:
Your contact: <a href="mailto:${object.user_id.email or ''}?subject=Invoice%20${object.number}">${object.user_id.name}</a>
% endif
</p>
% set signup_url = object.get_signup_url()
% if signup_url:
<p>
You can access the invoice document and pay online via our Customer Portal:
</p>
<a style="display:block; width: 150px; height:20px; margin-left: 120px; color: #DDD; font-family: 'Lucida Grande', Helvetica, Arial, sans-serif; font-size: 13px; font-weight: bold; text-align: center; text-decoration: none !important; line-height: 1; padding: 5px 0px 0px 0px; background-color: #8E0000; border-radius: 5px 5px; background-repeat: repeat no-repeat;"
href="${signup_url}">View Invoice</a>
% endif
% if object.paypal_url:
<br/>
<p>It is also possible to directly pay with Paypal:</p>
<a style="margin-left: 120px;" href="${object.paypal_url}">
<img class="oe_edi_paypal_button" src="/sale/static/img/btn_paynowcc_lg.gif"/>
</a>
% endif
<br/>
<p>If you have any question, do not hesitate to contact us.</p>
<p>Thank you for choosing ${object.company_id.name or 'us'}!</p>
<br/>
<br/>
<div style="width: 375px; margin: 0px; padding: 0px; background-color: #8E0000; border-top-left-radius: 5px 5px; border-top-right-radius: 5px 5px; background-repeat: repeat no-repeat;">
<h3 style="margin: 0px; padding: 2px 14px; font-size: 12px; color: #DDD;">
<strong style="text-transform:uppercase;">${object.company_id.name}</strong></h3>
</div>
<div style="width: 347px; margin: 0px; padding: 5px 14px; line-height: 16px; background-color: #F2F2F2;">
<span style="color: #222; margin-bottom: 5px; display: block; ">
${object.company_id.partner_id.sudo().with_context(show_address=True, html_format=True).name_get()[0][1] | safe}
</span>
% if object.company_id.phone:
<div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; ">
Phone: ${object.company_id.phone}
</div>
% endif
% if object.company_id.website:
<div>
Web : <a href="${object.company_id.website}">${object.company_id.website}</a>
</div>
% endif
<p></p>
</div>
</div>
]]></field>
</record>