I delayed Barbarossa once and tried to knock the UK out and pushed into Africa and slowly made it to Iceland and Greenland while I maintained 200+ relations with the Soviets and had minimal forces on our border, and about 1943-44 out of the blue they declared war on me and they almost barreled through my forces and my forces were utterly crushed. Mind you I had very little on my border but when I reinforced and had attacked with numeral superiority they seemed unbeatable, and I lost that game I'm perhaps not the best person to respond to your question but I thought I'd give you my 2 cents.
Thanks for the input but, I however am keeping the Soviet border well garrisoned not to mention Japan has won in China thus the Soviets have to deploy a large amount of forces to Watch them not to mention the Turkish border because they also sided with me.
delaying barbarossa is one of the most fun experiences ever: its hitler saying "one at a time". however, there are ways to mess it up:
-you expect the soviets to truce you indefinitely
-you get attacked first
-the soviets outnumber you 10 to 1 (literally)
and for all these flaws it makes it a difficult thing to pull off. however, i once tried it and succeeded, even if it meant that after the allies truced me i was facing the full power of the soviet union, glorious 1000 divs strong and over 50 armored.
here are some pointers that might help:
-do NOT ally with romania. this makes the soviets simply forget about attacking through southern europe and is the best option in the long run. that romanian soviet truce is your most powerful fortification.
-establish a non agression pact with them. that way when they break it you know they are readying themselves.
-as soon as poland falls and the spoils are divided, fortify your entire front line with forts and infrastructure. if done correctly those forts should be lvl 10 by 1943ish, which is perfect. if possible and if IC permits it, establish more forts towards your rear as well and infra them too. if the pressure from the russians is too much, withdraw to your secondary lines.
-start the nuclear research as soon as the game allows you to. you might not get a nuke before '44, but by then you will be using them against the russian stacks of doom, so its ok.
if things play out normally, as in you are still at war with the UK and probably the US, it wont change much. just keep a few divs ready to repel any possible landings, and watch your italian allies, because they have a tendency of screaming "I SURRENDER" the moment they see an american point their fingers at them and saying pew pew.
if the allies are at peace with you, then youre in luck, as they (unlike our commie cronies) wont break that truce. make sure you always keep a minimum of 12 divs per fortified province. the reason for this is not one of actually winning against them (if they attack, the fortifications will crumble quite fast), its all about disuation. if the AI sees 12 divs of literally anything on a lvl 10 fort, they simply refuse to attack, even if they could hipothetically win. the same thing happens as germany: you COULD take the marginot line through assault (ive done it, but damn i dont reccomend it XD), but its far more efficient to go around it. the AI however, has no other way around it, and it ends up turning into something quite similar to ww1: 2 trenches facing each other but noone attacks. also, the russian nuclear program will certainly not be their biggest priority, so take your time with that.
of course, if you dont want to do the armageddon scenario, you can try to tackle them with your army, but that is seriously next to impossible, unless you attack a province from 3 sides with top tier infantry armed with artillery and engineers or other brigades, supported by HQ's and with 24 per province. you will literally try to attrition the soviets, which is not impossible, but again, its impractical. i once managed to destroy around 300 russian divs (according to my intelligence, not my reliable source) through sheer constant attacks into premzyl. the russians and i got into some titanic struggles there, but the russians were in an almost total disadvantage and took many times my losses. every time i came close to conquering it i withdrew and regrouped, then attacked again, forcing the AI to feed more and more men there. eventually after 3 months of constant combat i managed a breakthrough and encircled the soviet southern front, but my manpower was almost exhausted (i never do extended mobilization no matter what, unless im pushed to the gates of berlin) and the soviets mobilized again, turning my efforts into another slugger match. after that i simply decided to nuke them into oblivion, a process that took nearly 2 years.