This was published for the Leafs 100th year (2016-17) and is the best source on Leafs history.
If you want a brief-ish recent summary:
Early 2008, the Maple Leafs decided it was time to rebuild. Former GM Cliff Fletcher had returned as interim GM. The aging core known as the Muskoka Five (Sundin, Kaberle, McCabe, Tucker, and Kubina) was not good enough to contend for a cup. However, they didn’t want to leave the team and had NTCs in place that made trading them difficult. Sundin refused to waive and left as a free agent. Tucker was traded to Colorado, McCabe to Florida, Kubina (later) to Atlanta — all for scraps. Kaberle was very resistant to being traded and remained on the team. Fletcher drafted Luke Schenn 5th overall, and was soon replaced by Brian Burke.
Burke did not believe in a traditional rebuild. He had a five-year plan to retool the team (this effectively delayed the real rebuild until 2015 when the Leafs decided to blow up the core Burke had assembled and drafted Marner). Among his most notable moves, Burke drafted Kadri 7th overall, traded two firsts and a second for Kessel, traded scraps for Phaneuf, signed Komisarek, signed Beauchemin and soon after traded him to Anaheim for Lupul and Gardiner, traded Kaberle for a 1st, Colborne, and a 2nd, drafted Rielly 5th overall, and traded Schenn for JVR.
Burke’s strong point was his trading. His free agent signings were bad and often reactionary. Leafs need defence? Sign Komisarek to 4.5x5. Leafs need a centre and missed out on Brad Richards? Sign a past-it Tim Connolly. His drafting was even worse. Burke loved big, gritty Americans. He nearly always took size over skill. Over four drafts, only 5/29 players became NHLers (Rielly, Kadri, Brown, Leivo, Sparks). And the former two were drafted 5th and 7th overall, respectively.
Burke was very stubborn and refused to fire his friend and head coach Ron Wilson until well past his expiration date.
Burke was fired before the lockout season abruptly; his protege assistant GM Nonis took over and only made things worse. He traded for Bernier after Reimer took us to the playoffs with his best season yet, traded three picks for Dave Bolland who left a season later. The thing about Nonis was that all his trades were far less impactful than those of Burke, but his drafting and signings weren’t any better either. He signed David fucking Clarkson to 5.25x7 and attempted to re-sign Bolland at 5x5.
Brendan Shanahan is hired as president of the Leafs in 2014, after the season ended and the Leafs finished 23rd. He makes no immediate changes. The Leafs draft William Nylander. In the summer, assistant GMs Dave Poulin and Claude Loiselle are fired, but Nonis stays on. Shanahan hires Kyle Dubas, Mark Hunter, and Brendan Pridham.
The Leafs have a decent record until January, where it all collapses. Randy Carlyle is fired and replaced by Peter Horachek, under whom the Leafs do even worse. The players are very obviously not playing to the best of their ability. Immediately after the season ends, Shanahan fires Nonis, the director of player development, the entire coaching staff, and 16 scouts. He fills out the staff with well-respected fresh faces. The Leafs draft Marner. Dubas, acting as interim GM trades Kessel, albeit for an underwhelming return while retaining salary, due to having only one interested partner in the Penguins. Shanahan is later quoted making a joke about “trading away your problems to Pittsburgh.” Lou Lamoriello is hired as GM, and Mike Babcock is hired as head coach. The Leafs change their logo to something more akin to the classic design. Lou helps the Leafs get out from their worst remaining contract, trading Phaneuf without retaining any salary. Matthews is drafted. Lou trades for Andersen. Dubas succeeds him, signs Tavares. The rest is history.
Edit: added more details.
The Centennial Publication. https://www.amazon.ca/Toronto-Maple-Leaf-Hockey-Club/dp/077107929X
The Toronto Maple Leaf Hockey Club: Official Centennial Publication https://www.amazon.ca/dp/077107929X/ref=cm_sw_r_cp_api_glt_i_BANP28FJSP3W7VBEPR5X