If you are concerned about this issue, you can use Route 53 and ELB together to get what you want. Create the
www record as an A record, then select the "Alias" option and the interface will allow you to select an AWS-specific target to point the record to. So the ELB has to exist first, then you can create the Alias to it.
So you start to create a new A record in Route 53 as usual, but you click on the "Alias" option right under the host name. The freeform text block will disappear and you will be given the ability to select your ELB under "Alias Target". Select your ELB and save the change. You will then have an A record that points to www, which will be your ELB.
(The above info about the Route 53 UI has been corrected from the original error.)
This is a special Route 53 feature most often used to handle serving from the domain apex, where A records are required. But it can also be used for subdomains such as
www. Basically, it's an A record that acts like a CNAME within the confines of AWS. Using this feature, DNS tools will find an A record.