For starters, this projection will be purely electoral college based, relying entirely on polling and nothing else, as opposed to say FiveThirtyEight, which employs a nifty "polling plus" forecast. Why not just rely on Pollster, or Real Clear Politics, you might ask? While both sites are exemplary, RCP excludes some surveys, and Pollster has yet to start projections for individual states in the general election - not to mention both sites aren't quite as up-to-date with the latest polling information as I would like them to be.
At least for now, each state's electoral college projection will be based on every state poll released in the last two months. For example, today's update would be based on polling dating back to December 25, 2015. Obviously, as the pace of general election polling picks up through the rest of the year, the projection will be based on a smaller time frame.
Since we're still nine months from the presidential race, very little general election polling has been done in most states, while other states have seen no polling at all. Regarding states that have not had any polls conducted over the last two months, the electoral college projection will be based on an average of the most recent survey conducted after Trump's June 2015 presidential announcement, and any survey conducted within one month of that most recent poll. If there has been NO polling post Trump-announcement, the electoral college projection will be based on an average of that state's 2004 and 2012 presidential election results. I've chosen 2004 and 2012 as a baseline in the absence of any polling because these two elections featured a relatively moderate-to-small win for the two political parties - the Republicans won by 2.5 nationally in 2004, while the Democrats won by 3.9 points in 2012.
Electoral college projections will be made for the three most likely GOP nominees (Trump, Rubio, and Cruz) using various shades of blue (for Democrats) and red (for Republicans), based on the Republican candidate's lead or deficit against the Democratic candidate. For example, the darker the shade of red, the stronger the Republican's lead against Hillary Clinton. The lighter the shade of blue, the smaller Hillary Clinton's advantage against the Republican candidate. For an illustration, see the map below:
Now, on to the projections...starting with the strongest Republican candidate, based on current polling: