Get the Provisioning Template

using (Context ctx = new ClientContext(<siteUrl>))
{
    string TemplateFilename = "<FileName>.xml";
    ctx.Load(ctx.Web, w => w.Lists, w => w.Folders);
    Microsoft.SharePoint.Client.File templateFile = ctx.Web.Lists.GetByTitle("Site Assets").RootFolder.Folders.GetByUrl("Templates").GetFile(TemplateFilename);
    ctx.ExecuteQuery();
    FileInformation fileInfo = Microsoft.SharePoint.Client.File.OpenBinaryDirect(ctx, templateFile.ServerRelativeUrl);
    assetContext.ExecuteQuery();
    filePath = Path.GetTempPath() + "\\" + TemplateFilename;
    using (var fileStream = new FileStream(filePath, FileMode.Create))
        fileInfo.Stream.CopyTo(fileStream);
}

using (FileStream fs = System.IO.File.OpenRead(filePath))
{
    ITemplateFormatter formatter = XMLPnPSchemaFormatter.LatestFormatter; //Use the same version as the PnP template
    Template = formatter.ToProvisioningTemplate(fs);
}