I have few subdomains in a site. Like secure.mysite.com, support.mysite.com, blog.mysite.com. In sitemap.org FAQ, i have seen we should create different subdomains for sitemaps. So how shall i use it? Is it like secure.mysite.com/sitemap.xml support.mysite.com/sitemap.xml blog.mysite.com/sitemap.xml If I have same page under main domain and subdomain, can i include both in sitemap after setting canonical tag? Please advice.
Yes you can include. But why don't you redirect those urls to the main one. Still if you've some same pages in all of your websites like About Us/Contact US/ than you can you canonical issue. But according to Matt Cutts duplicate content won't hurt.