Our marketing department has decided that a new site with new content is needed to launch new products and support our existing ones. We cannot use the same subdomain(www = old subdomain  and ww1 = new subdomain)as there is a technically clash between the windows server currently used, and the lamp stack required to run the new wordpress based CMS and site. We also have an aging piece of SAAS software on the www domain which is makes moving it to it's own subdomain far too risky. 301's have been floated as a way of managing the transition. I'm not too keen on that idea due to the double effect of new subdomain and content, and the SEO impact it might have. I've suggested uploading the new site to the new subdomain while leaving the old site in place. Then gradually migrating sections over before turning parts of the old site off and using a 301 at that point to finalise the move. The old site would inform user's there is a new version and it would then convert them to the new site(along with a cookie to auto redirect them in future.) while still leaving the old content in place for existing search traffic, bookmarks and visitors via static URLs. Before turning off sections on the old site we would create rel canonicals to redirect to the new pages based on a a mapped set of URLs(this in itself concerns me as the rel canonical is essentially linking to different content). Would be grateful for any advice on whether this strategy is flawed or whether another strategy might be more suitable?