There appears to have been only 2 Edwin Greenalls [any spelling] with births registered between Q1[Mar] 1899 to Q4[Dec] 1901. One was in Prescott district, Lancashire, the other in West Ham district of Essex.. The Essex one fits with your "from London" statement.
GRO reference = Greenhall Edwin Q3 [Sep] 1900, District West Ham, Vol 4a, page 124
See FreeBMD web site.
Note: Your reference to Cannon could be Cann Hall, a civil parish of South Leyton, which is a sub-district of the registration district of West Ham.
From the 1901 census at http://www.1901census.nationalarchives.gov.uk
, census place West Ham
Name surname; age; where born ;admin county; civil parish; occupation
William Greenall; 29; Essex, Tidal Basin; West Ham; West Ham; Gas Stoker
Sarah Greenall; 26; Essex, Tidal Basin; West Ham; West Ham;
Grace Greenall; 4; Essex, Tidal Basin; West Ham; West Ham;
Sarah Greenall; 3; Essex, Tidal Basin; West Ham; West Ham;
William Greenall; 2; Essex, Tidal Basin; West Ham; West Ham;
Edwin Greenall; 1; Essex, Tidal Basin; West Ham; West Ham.
To find the address you will either have to download the page image [charge] or post on the Topics > Census > UK > census of 1901 [just seen your other post and reply - possibly Margaret Panozzo can access it]
Note: Tidal Basin, Essex, was originally known as Plaistow Marsh and became an industrialised 'Royal Docks' area of south West Ham, now in London E16. The area suffered heavy bombing in the Blitz of WWII.
As for his service records as his birth was registered during the 3rd quarter 1900, he could have joined the Royal Navy some time after June to September 1918 [possibly a little earlier, but not serve in war zone]. If your lucky and he joined between then and 1923, his "service record" should be at the National Archive, London in document series ADM188. These are Service Registers and give place & date of birth, physical characteristics on entry and a summary of service up to 1927. The registers are in numerical order [service number], but there is a name index.
If you need to use a researcher see the National Archives web site at http://www.nationalarchives.gov.uk/
, from home page see Home > Getting Started > list if Independent researchers; you will see a few have website that will enable you to judge what services they offer and costs.
If he joined after 1923 he would have been given his service record when he was discharged. The Royal Navy only retained some details, mainly for pension purposes, so the only information they will hold is his Service details (number, rank, name etc) and a list of dates and ships/shore bases served. Any request must be by [or with written consent of] the Next of Kin and proof of death. A charge may be made for enquiries and "family history" has a low priority. See the Veterans Agency at http://www.veteransagency.mod.uk/